Conventionally, heat-shrinkable polyester films have been used in a wide variety of uses such as shrinkable wrapping materials, shrinkable labels and the like owing to the property of shrinkage by heating. Among them, oriented films such as poly(vinyl chloride) type films, polystyrene type films, polyester type films have been used as labels and cap seals for various containers such as polyethylene terephthalate (PET) containers and glass containers, or for integral wrapping.
However, for example, the poly(vinyl chloride) type films have a problem that the films are inferior in heat resistance, emit hydrochloric acid gas at the time of incineration, and generate substances possible to convert into dioxins. Also, in the case heat-shrinkable poly(vinyl chloride) type resin films are used for shrinkable labels for PET containers or the like, there is a problem that the labels have to be separated from containers for recycling the containers.
On the other hand, the polystyrene type films can be evaluated highly in terms of good finishing appearances after shrinkage, but they are inferior in solvent resistance so that specific ink compositions have to be used for printing. With respect to polystyrene type resins, there is another problem that it is needed for the resins to be incinerated at a high temperature and a large quantity of black smoke and malodorous gas are emitted at the time of incineration.
It is therefore highly expected that the polyester type films free from such problems are to be used as shrinkable labels in place of the poly(vinyl chloride) type films and polystyrene type films, and along with increase of the use of PET containers, their use tends to be increased. However, it is required also for the conventional heat-shrinkable polyester type films to be improved more in the properties.
For example, in the case of using the films as labels of beverage-containing PET containers and vending the beverage by an automatic vending machine, there occurs a problem that the slipping property of the labels is so insufficient as to cause clogging in the machine, that is, goods cannot pass in the path and reach the exit slot of the machine or that several good are discharged simultaneously and accordingly, the slipping property of the films is required to be good from users.
As a countermeasure to the problem, a method of laminating layers with good slipping properties on film surfaces have been employed (e.g. reference to Japanese Patent Laid-Open Publication No. 2002-196677).
However, as a new problem of such treatment, stain adhesion of wear debris of films to contact rolls at the time of labeling work or to label contact parts in the automatic vending machine takes place.
In addition, recently, shrinkage labels tend to be used increasingly for the purpose of protecting the contents of containers from ultraviolet (UV) rays. Conventionally, UV ray-cut type poly(vinyl chloride) films have been used, but it has been required to urgently develop other materials for cutting UV rays. Although it depends on the contents, it is very important that the UV ray-cutting capability is to cut UV rays in a longer wavelength range, particularly in a range from 380 nm to 400 nm, since the contents are denatured or colored in the longer wavelength range of UV rays, that is, from 360 nm to 400 nm, in the case of food and beverages. In the case of using these heat-shrinkable films, normally, after designs are printed in the inside of the labels, white printing is carried out (e.g. reference to Japanese Patent Laid-Open Publication No. 11-188817).
The above-mentioned white printing is to be set in the sides of the labels to be brought into contact with PET bottles in the case of threading the labels to the bottles, the white printing is very important to have good slipping property to PET bottles. If the slipping property is inferior, the labels are shrunk in upper parts of the bottles before they move to prescribed positions where they are to be shrunk to result in production loss. Generally, it is common to attach labels after PET bottles are filled with a beverage and the bottle surface bears water droplets. Since the insertion resistance is higher in the state that the bottle surface is wet than in the state the bottle surface is dry and accordingly, there is a problem that the value of the insertion resistance is changed depending on the types of white printing.
Moreover, the thickness of white printing ink layer is generally about 3 μm and insufficient to shield light rays. Although it is tried to shield light rays by carrying out white printing two times, it is disadvantageous in terms of the quality (alteration of shrinking properties owing to thickness of the ink layer), the time limit of shipment, and the cost.